The present invention relates to compositions and processes for protecting the surface of receptacles having a refractory surface or lining to prevent molten slag and molten metal from adhering to or penetrating the refractory.
Surfaces of receptacles for processing and transporting molten metals such as molds, slag pots, and tundishes are often easily damaged by molten metal and the corresponding molten slag. The damage which results generally occurs because the molten material adheres to the walls of the receptacle and it fails to discharge when the slag layer is poured into a slag receiving pit as is common in the metal processing industry. To loosen the solidified material, or "skull" as it is commonly referred to in the industry, the receptacle has to be repeatedly beaten or otherwise jolted. This repeated abusive treatment of the receptacles leads to excessive deterioration. The same phenomenon applies to molten steel in ingot molds, with adhesion requiring excessive force for the ingot removal and damage to the molds. Further, the molten metal itself can damage the receptacle walls over time.
While the receptacles can be cleaned chemically through the use of acid solutions, such cleaning methods are highly undesirable from an environmental standpoint. Still further repeated use of acid solutions can cause damage to the receptacle walls over time.
In an attempt to solve these problems various compositions have been used to protect the walls of containment vessels from making contact with molten metal and molten slag. For example, U.S. Pat. No. 3,023,119 discloses that combinations of MgO and Al.sub.2 O.sub.3 are known as coatings for handling molten plutonium. This patent teaches that CaF.sub.2 is useful for coating metal or nonmetal receptacles used for molten plutonium. Likewise, U.S. Pat. Nos. 3,035,318 and 3,227,433 disclose the use of CaF.sub.2 as a coating to line vessel walls. The use of Al.sub.2 TiO.sub.3 and Al.sub.2 O.sub.3 TiO.sub.3 as coatings for coating crucibles for molten uranium and uranium alloys is also known according to U.S. Pat. Nos. 3,890,140 and 3,915,695.
The use of such materials to prevent contact between the molten metal and the underlying receptacle material however, usually results in the need to use excessively thick layers due to the tendency of some of these materials to dissolve or react with the molten metal. Any interactions between the coating layer and the molten metal may lead to contamination of the metal.
Still other coatings for receptacles used to contain liquid and molten metals are known. For example, U.S. Pat. No. 4,901,984 which issued Feb. 20, 1990 to Daussen et al., discloses a method for coating a vessel and the coating obtained by the method. The method involves providing a permanent refractory lining on which there is deposited a refractory wearing layer including inorganic particles and a binder. Initially, a layer of silicon resin, which is impenetrable to water, is applied over a permanent refractory lining layer, then the wearing layer which is typically made from inorganic particles and the binder is applied over the water impenetrable layer. All of the layers are then subjected to sufficient drying to remove any water or hydrogen containing compounds.
While, the general concept of coating receptacles for processing molten metals is known in the art, none of the art known to the inventors of the present invention include compositions which utilize slag fines for preparing the coating compositions.
Slag is formed during metallurgical processing as the fused product of oxidized impurities and a fluxing agent added to the molten metal, such as lime. In the steel industry for example, slag is the neutralized product of anhydrous compounds entering into the process. The slag tends to float to the top of the molten metal thus protecting the molten metal from oxidation and impurities such as phosphorous, among others. Eventually the slag is poured off or otherwise removed from the receptacle. Other than some value as a course aggregate in concrete or ballast, until now, slag has had limited commercial value and has merely been considered a by product of the steel processing industry. Typically, the slag fines which are formed during slag processing and screening, are subsequently stockpiled for later disposal via landfilling. Thus, while slag may be useful in construction applications, the slag fines have heretofore been costly to dispose of. It would thus be beneficial to use the slag generated during steel processing, rather than simply landfilling the slag.